There has been disclosed a control device for a DC motor including a power converter which supplies DC power to a DC motor; and rotating coordinate conversion means for performing a conversion from a two-phase rotation axis into a three-phase axis in order to control the power converter, the two-phase rotation axis being detected at each predetermined sampling time and having at least a rotation angle of the DC motor as a coordinate conversion angle, in which the control device is provided with first rotation angle compensating means for adding a rotation angle delayed according to the sampling time to at least the rotation angle of the DC motor detected at each predetermined sampling time, and the rotation angle resulting from the addition is set as the coordinate conversion angle.
However, the control device has the problem of rendering a control system unstable because of being unadaptable for a reduction in a phase margin due to characteristics inherent in the motor.